The present invention relates generally to pallet rack storage systems and more particularly, to pallet return pallet rack storage systems that selectively, efficiently and automatically return unloaded carts and pallets from a storage position where they may be unloaded to a return or loading position where they may be reloaded.
An important consideration in the storage or warehouse industry is the ability to safely and efficiently load and unload stored products while maintaining the highest possible storage density within a particular storage area. To this end, storage systems have been developed that utilize wheeled carts which ride on spaced, parallel rails. The wheeled carts are designed to carry and support the pallets and the loads that are placed on the pallets. Systems of this type are generally designed to accommodate a number of carts (and associated pallets and loads) and are referred to as pushback rack systems. These systems generally operate on a first in, last out inventory basis; that is, both loading and unloading take place from the same access aisle.
One such system, for example, is described in U.S. Pat. No. 4,773,546. In this system, multiple wheeled carts are provided which are designed to carry pallets and their loads. The wheeled carts roll on a pair of spaced, sloping, parallel rails and are proportioned to permit the multiple carts to overlap one another when in a forward, unloaded position. In operation, a pallet and load is placed on an upper cart. To store a second load, the second load is used to push the first cart and load rearward and the second load is placed on a lower cart. In a three deep system, a third load may be used to push the first and second carts rearward and the third load and pallet placed on the rails. The process is reversed for unloading. Efficient storage of multiple pallets, as well as increased storage density, is achieved with this system.
Another known pushback rack system having wheeled carts in rolling engagement with spaced, parallel rails is disclosed in U.S. Pat. No. 4,915,240. Pushback rack systems of this type utilize an increased number of wheeled carts without the necessity for increasing the number of rails, which is accomplished by using interlocking cart wheels which ride on the same rail rolling surface. In this manner, a single storage bay and/or pair of rails provides convenient and efficient storage of pallets and their loads that are multiple pallets deep. Improved storage density is provided while fewer access areas are required so that efficiency, ease of access and capacity is increased.
In the use of pushback rack systems, the carts are generally loaded and unloaded from the same access aisle. As a result, empty or broken pallets have to be physically removed from the carts by the operator and stored for re-use or discarded. In certain types of warehousing operations, this may decrease the efficiency of the loading/unloading process and increase the possibility of injury to the operator and damage to the equipment. Moreover, storage systems of this type cannot be readily adapted to operate under the first in, first out inventory basis.